Toner preloaded magnetic brush development system

ABSTRACT

This invention concerns magnetic brush development. A biased electrode is spaced from a magnetic roller at a location just prior to the roller entering a source of developer (containing toner particles on magnetic carriers). Developer is supplied between the magnetic roller and electrode whereby toner from the developer is attracted to the magnetic roller. As the roller rotates to the developer source developer is attracted to the magnetic roller and then is presented to a latent image on a photosensitive surface. Because the magnetic roller has been preloaded with toner prior to attracting developer from the developer source, this magnetic brush development system results in enhanced as well as quick development.

United States Patent 1 1 11 1 1,864

Hudson Oct. 14, 1975 [54] TONER PRELOADED MAGNETIC BRUSH 3,662,7115/1972 Hudson 118/637 DEVELOPMENT SYSTEM 3,724,422 4/1973 Latone et a1 118/637 3,754,526 8/1973 Caudill 118/637 [75] Inventor: Frederick W.Hudson, West Henrietta Primary ExaminerMervin Stein [73] Assignee: XeroxCorporation, Stamford,

C [57] ABSTRACT This invention concerns magnetic brush development. [22]Filed 1973 A biased electrode is spaced from a magnetic roller at 1 1 pp324,467 a location just prior to the roller entering a source ofdeveloper (containing toner particles on magnetic car- 52 US. 01118/637; 117/175 Tiers) Developer is Supplied between the magnetic 51Int. c1. G03G 15/09 roller and electrode whereby tone from the developer[58] Field of Search n 1 18/636 637 24; is attracted to the magneticroller. As the roller rotates 117/175 to the developer source developer1s attracted to the magnetic roller and then is presented to a latentimage [56] References Cited on a photosensitive surface. Because themagnetic roller has been preloaded with toner prior to attracting UNITEDSTATES PATENTS developer from the developer source, this magnetic31203394 8/1965 p et 118/637 brush development system results inenhanced as well 3,443,517 5/1969 Gundlach 117 17.5 as quickdevelopment. 3,572,289 3/1971 Maksym1ak.... 118/637 3,641,980 2/1972Bickmore 118/637 11 Claims, 3 Drawing Figures U.S. Patent 0a. 14, 1975Sheet 1 of2 3,911,864

US. Patent Oct. 14, 1975 Sheet2 0f2 3,911,864

TONER PRELOADED MAGNETIC BRUSH DEVELOPMENT SYSTEM DESCRIPTION Thisinvention relates to enhancing development of an electrostatic latentimage and increasing development speed when utilizing a magnetic brushdevelopsystem.

It is an object of the invention to achieve the above by supplying tonerparticles to a magnetic roller just prior to the roller attractingdeveloper thereto for presenting to a latent image.

The details of the invention can be understood from the followingdescription with reference to the drawing wherein:

FIG. 1 is a view of a general xerographic copying system;

FIG. 2 is a detailed view of one embodiment of the invention; and

FIG. 3 is a view of another embodiment of the invention;

Shown in FIG. 1 is a xerographic machine employing the magnetic brushdevelopment apparatus of the instant invention. The elements of thismachine, which are constructed for continuous and automatic operation,are all conventional in the xerographic art except for the noveldevelopment apparatus, which forms the basis of the instant application.For the purpose of the present disclosure. the several xerographicprocessing stations in the path of movement of the xerographic surfacemay be briefly described as follows:

A charging station A, at which a uniform electrostatic charge isdeposited on the photoconductive layer of the xerographic surface;

An exposure station B, at which the light or radiation pattern of copyto be reproduced is projected onto the xerographic surface to dissipatethe charge in the exposed areas thereof to thereby leave a latentelectrostatic image of the copy to be reproduced;

A developing station C, at which a xerographic developing matcrial,including toner particles having an electrostatic charge opposite tothat of the electrostatic latent image, are moved into contact with theimage bearing surface, whereby the toner particles adhere to theelectrostatic latent image to form a xerographic powdered image in theconfiguration of the copy being reproduced;

A transfer station D, at which the xerographic powder image iselectrostatically transferred from the xerographic surface to a transfermaterial or a support surface; and

A cleaning and discharge station E, at which the xerographic surface isbrushed to remove residual toner particles remaining thereon after imagetransfer, and at which the surface is exposed to a relatively brightlight source to effect substantially complete discharge of any residualelectrostatic charge remaining thereon.

The latent electrostatic images to be developed are formed on aphotosensitive surface l formed in the shape of an endless belt. ThesurfaceIO could be of any configuration including a disposablephotoconductive web or sheets as well as a drum shaped reusablephotoconductor. The belt is adapted to be rotated about three supportingrollers l2, l4 and 16, two of which, 14 and 16 are idler rollers and thethird of which, 12, is a power imparting roller driven by any convenientpower source 18. The movement of the photosensitive surface permits itssurface to be moved past the various xerographic processing stationsincluding the development zone C.

Referring now to FIG. 2, the xerographic developing apparatus isprovided within a developer housing 20 formed of a non-magneticmaterial. The lower portion of the housing is trough-like inconfiguration to define a sump 22 to support a quantity of two-componentmagnetic developer mix 24. The developer employed includes imagedeveloping toner particles and larger carrier granules having magneticproperties. The carrier granules may be metallic or other materialshaving magnetic properties either uncoated or coated with a carriercoating material so that a triboelectric charge is generated between itand the toner upon mutual interaction. This charge is necessary toeffect the xerographic development of the images. Examples of suchmagnetic developer are described in US. Pat. No. 2,874,063 to Greig.

Located within the housing 20 are a plurality of magnetic rollers whichcomprise non-magnetic rotatable hollow cylinders 26, 28, 30, 32 and 34arranged to rotate in alternating directions.

Each of these cylinders has an associated gear member (not shown) forimparting the alternating directions thereto. The gears employed forrotating the cylinders are connected to a suitable source of power, notshown, for imparting motion thereto. This mechanism can be the same asshown in FIG. 2 of US. Pat. No. 3,572,289 to Maksymiak.

Located within each of the cylinders is a magnet 36, preferablypermanent, with north and south poles extending the length of themagnetic cylinders with their field producing poles facing in thedirection over which the developer will be moved. For example, withincylinders 26, 30 and 34, the poles of the magnets face toward thephotoconductor surface to be developed for the presentation ofdeveloping material to the image. The field producing-magnets of thecylinders 28 and 32, which function to merely transport the developer,have their field producing poles in a direction away from thephotoconductive surface. Thus, when the cylinders are rotated, magneticdeveloper will be entrained by the magnetic fields emanating through therotating cylinder 26 to cause developer to move in brushing contact withthe photoconductive surface.

Upon reaching the uppermost position of cylinder 26, the magneticdeveloper is passed beyond the effect of the magnetic field of cylinder26 into the effect of the magnetic field emanating from the nextadjacent roller 28. In this manner, the developer may be magneticallyattracted and then conveyed between adjacent cylinders from theuppermost position of a lower cylinder to the lowermost position of thenext higher sylinder. This procedure continues until the developercontacts the uppermost roller 34 whereafter, continued cylinder rotationwill permit the developer to be dropped onto a guide plate 38 inasmuchas it is no longer within the field of influence of any magnetic fieldproducing means. Located above the housing 20 is a well-known tonerreservoir or dispenser 40 containing toner particles 42 therein. Toneris dispensed from the housing onto the guide plate 38. Attached to theguide plate 38 are chutes 44 and 46 having inlet openings 48 and 50,respectively. The excess developer deposited on the plate 38 by the roll34 and the toner particles 42 discharged from the dispenser 40 slidedown the guide plate 38 with a portion thereof entering inlet openings48 and 50 of the chutes 44 and 46 and a portion thereof skipping overthe chute openings onto the lower end of the plate 38 and beingdischarged therefrom directly into the developer sump 22. The inletopenings 48 and 50 extend the length of the magnetic rollers and are ofsuch a width as to control the amount of developer entering thereintoand passing directly to the developer sump. The chutes 44 and 46 have anoutlet opening 52 and 54, respectively, which extend the entire lengthof the magnetic lower rollers 30 and 26. A pair of electrodes 56 and 58are provided at the lower end of the chutes 44 and 46, respectively, andare spaced from a respective roller 30 and 26. The electrodes are solocated relative to the chute openings that the developer dischargedthrough the openings will pass between a respective roll and electrode.A duct member 59 is positioned to direct the developer flowing betweenthe electrode 56 and roller 30 to the chute 46 where the developer joinsthe developer stream in chute 46 and passes between the electrode 58 androller 26. The electrodes are electrically separated from theirrespective chutes by an insulating member 60.

The electrodes 56 and 58 are coupled to a high voltage source ofsuitable electrical potential V whereby triboelectrically charged tonerfrom the developer material emerging from openings 52 and 54 and passingbetween the electrodes 56 and roll 30 and between electrode 58 and roll26 will be stripped from the carrier beads to develop or adhere to therollers 30 and 26. The rollers 26 and 30 are coupled to a suitableelectrical potential V2 of a magnitude and polarity that in conjunctionwith the electrodes, they will attract the toner from the carrier beadsand that the toner will be deposited on the charged latent image whilesuppressing background deposition of the toner. For instance, thepotential on the electrode V1 may be 8OO volts, the potential on therollers V2 may be +300 volts, the latent image charge may be +800 voltsand the background charge may be +200 volts and the polarity of thetriboelectrically charged toner may be negative. Obviously, the voltagepolarities may change in accordance with the polarity of the charge onthe image and toner.

In operation, as the roller 26 rotates, the developed portion thereofenters the developer mix 24 and as the surface thereof approaches themagnetic field imposed by magnet 36, carrier particles with theirassociated toner particles are attracted to the roller surface and thenpresented to the electrostatic latent image on the photosensitive beltfor development whereby toner will be stripped from the roller surfaceand from the carriers. Continued rotation of the roller 26 brings thesame surface to an attracting magnetic field of the conveying roller 28whereby the excess developer on roll 26 is transferred thereto and therest of the rollers as described previously. The developer remaining onthe upper roller 34 is discharged onto the plate 38 and is allowed tomix with the toner 42 and fiow by gravity into the chutes 44 and 46 oroff the plate 38 whereby the toner becomes properly charged, the denudedcarriers are retoned and the back portions of the development rolls 26and are developed with toners.

From the above it can be seen that since the surface of roller 26 isprecoated with toner particles, the rotational speed thereof through thedeveloper mix can be increased and still the same total amount of tonerwill be presented to the latent image as a roller rotated at a normalspeed which solely relies upon picking up toner when rotated through thedeveloper mix. By the time excess developer has passed to roller 30, thecarrier beads are substantially stripped of toner. Thus, it isespecially advantageous to precoat the roller 30 with toner. Also, byutilizing the principle of this invention, development of the image isenhanced when utilizing rotational speeds equal to or slightly greaterthan the speed normally used.

Referring to FIG. 3, the embodiment of FIGS. 1 and 2 is modified. Allelements which are the same as the previous embodiment are designated bythe same reference numeral only with an a affixed thereto. In thisembodiment a bucket conveyor is utilized to convey a portion of thedeveloper mix to an inlet opening of a split chute 104. The developer issplit into two streams, one down chute 104 and between the roller 26aand electrode 58a and the other down chute 106 directly to the developermix 24a. Since only one magnetic roller is used, the bucket conveyor isutilized for circulating and mixing the developer mixfThe magneticroller 26a is developed with toner in the same manner as the previousembodiment.

It should be realized that any number of magnetic rollers may beutilized with this invention and that in the embodiment of FIGS. 1 and 2either the roller 26 or the roller 30 may be developed with tonerwithout the other being developed with toner although it is preferred todevelop each roller. Also, all of the rollers may be rotated in the samedirection and each roller may present developer to the latent image.

I claim:

1. A magnetic brush development system for an electrostatic processor todevelop latent electrostatic images carried by a movable photosensitivesurface through the use of a developer containing oppositely chargedtoner and carrier particles; said system comprising the combination of asump for storing a supply of developer;

a rotatable member positioned between said sump and said photosensitivesurface for transporting developer in a predetermined direction fromsaid sump to said photosensitive surface, said rotatable member having amagnetic field emanating therefrom for loading developer on said memberas it advances past said sump and for retaining said developer on saidmember as it advances past said photosensitive surface;

an electrode positioned adjacent said rotatable member on a side thereofremote from said photosensitive surface, whereby successive portions ofsaid rotatable member are sequentially advanced past said electrode,sump and photosensitive surface when said member is rotated in saidpredetermined direction; and

means coupled to said electrode and said rotatable member forestablishing a potential difference therebetween of a polarity tendingto cause toner particles to adhere to said rotatable member prior to theloading thereof with developer.

2. The development system of claim 1 wherein excess developer isreleased from said rotatable member after passing said photosensitivesurface; said system further including a toner dispenser for supplyingadditional toner for said developer, and means for guiding at least apart of said excess developer and a part of said additional tonerbetween said electrode and said rotatable member.

3. The development system of claim 2 wherein all of the excess developeris guided between the rotatable member and said electrode.

4. The development system of claim 2 wherein only a portion of saidexcess developer and a portion of said additional toner are guidedbetween the rotatable member and said electrode; and further includingmeans for guiding the remainder of the excess developer and additionaltoner directly to the sump.

5. A magnetic brush development system for an electrostatic processor todevelop latent electrostatic images carried by a movable photosensitivesurface through the use of a developer containing oppositely chargedtoner and carrier particles; said system comprising the combination of aplurality of rotatable members extending in series from said sump alongsaid photosensitive surface, each of said members having a magneticfield emanating therefrom and being rotatable in a predetermineddirection for transporting developer from said sump along a path runningbetween said photosensitive surface and successive ones of said members;

a first electrode mounted adjacent one of said members remotely fromsaid photosensitive surface,

a second electrode mounted adjacent another of said members remotelyfrom said photosensitive surface, said other member being separated insaid series from said one member by at least one intervening member;

means for guiding developer between said first electrode and said onerotating member and between said second electrode and said otherrotating member;

means coupled to said first electrode and said one member forestablishing a potential difference therebetween of a polarity tendingto cause said one member to attract toner from the developer guidedtherebetween; and

means coupled to said second electrode and said other member forestablishing a potential difference therebetween of a polarity tendingto cause said other member to attract toner from the developer guidedtherebetween.

6. The development system of claim 1 further including another rotatablemember positioned between said sump and the first mentioned rotatablemember for transporting developer from said sump to said first mentionedmember.

7. The structure as recited in claim 6 'wherein excess developer isreleased from said rotatable member after passing said photosensitivesurface; and further including means for routing at least a portion ofsaid excess developer between said rotatable member and said electrode.

8. The development system of claim 1 further including at least twoadditional rotatable members in series with the first mentionedrotatable member, each of said additional members having a magneticfield emanating therefrom to assist in transporting developer from saidsump to said photosensitive surface.

9. The development system of claim 8 wherein excess developer isreleased from a final rotatable member of said series after passing saidsurface; and further including means for adding additional toner to saiddeveloper, and guide means for guiding at least a portion of said excessdeveloper and a portion of said additional toner between said firstmentioned rotatable member and said electrode.

10. The development system of claim 9 wherein said guide means guides apart of said excess developer and a part of said additional tonerdirectly to said sump.

11. The structure as recited in claim 1 wherein said rotatable membercomprises a roller and a permanent magnet.

1. A magnetic brush development system for an electrostatic processor todevelop latent electrostatic images carried by a movable photosensitivesurface through the use of a developer containing oppositely chargedtoner and carrier particles; said system comprising the combination of asump for storing a supply of developer; a rotatable member positionedbetween said sump and said photosensitive surface for transportingdeveloper in a predetermined direction from said sump to saidphotosensitive surface, said rotatable member having a magnetic fieldemanating therefrom for loading developer on said member as it advancespast said sump and for retaining said developer on said member as itadvances past said photosensitive surface; an electrode positionedadjacent said rotatable member on a side thereof remote from saidphotosensitive surface, whereby successive portions of said rotatablemember are sequentially advanced past said electrode, sump andphotosensitive surface when said member is rotated in said predetermineddirection; and means coupled to said electrode and said rotatable memberfor establishing a potential difference therebetween of a polaritytending to cause toner particles to adhere to said rotatable memberprior to the loading thereof with developer.
 2. The development systemof claim 1 wherein excess developer is released from said rotatablemember after passing said photosensitive surface; said system furtherincluding a toner dispenser for supplying additional toner for saiddeveloper, and means for guiding at least a part of said excessdeveloper and a part of said additional toner between said electrode andsaid rotatable member.
 3. The development system of claim 2 wherein allof the excess developer is guided between the rotatable member and saidelectrode.
 4. The development system of claim 2 wherein only a portionof said excess developer and a portion of said additional toner areguided between the rotatable member and said electrode; and furtherincluding means for guiding the remainder of the excess developer andadditional toner directly to the sump.
 5. A magnetic brush developmentsystem for an electrostatic processor to develop latent electrostaticimages carried by a movable photosensitive surface through the use of adeveloper containing oppositely charged toner and carrier particles;said system comprising the combination of a plurality of rotatablemembers extending in series from said sump along said photosensitivesurface, each of said members having a magnetic field emanatingtherefrom and being rotatable in a predetermined direction fortransporting developer from said sump along a path running between saidphotosensitive surface and successive ones of said members; a firstelectrode mounted adjacent one of said memberS remotely from saidphotosensitive surface, a second electrode mounted adjacent another ofsaid members remotely from said photosensitive surface, said othermember being separated in said series from said one member by at leastone intervening member; means for guiding developer between said firstelectrode and said one rotating member and between said second electrodeand said other rotating member; means coupled to said first electrodeand said one member for establishing a potential difference therebetweenof a polarity tending to cause said one member to attract toner from thedeveloper guided therebetween; and means coupled to said secondelectrode and said other member for establishing a potential differencetherebetween of a polarity tending to cause said other member to attracttoner from the developer guided therebetween.
 6. The development systemof claim 1 further including another rotatable member positioned betweensaid sump and the first mentioned rotatable member for transportingdeveloper from said sump to said first mentioned member.
 7. Thestructure as recited in claim 6 wherein excess developer is releasedfrom said rotatable member after passing said photosensitive surface;and further including means for routing at least a portion of saidexcess developer between said rotatable member and said electrode. 8.The development system of claim 1 further including at least twoadditional rotatable members in series with the first mentionedrotatable member, each of said additional members having a magneticfield emanating therefrom to assist in transporting developer from saidsump to said photosensitive surface.
 9. The development system of claim8 wherein excess developer is released from a final rotatable member ofsaid series after passing said surface; and further including means foradding additional toner to said developer, and guide means for guidingat least a portion of said excess developer and a portion of saidadditional toner between said first mentioned rotatable member and saidelectrode.
 10. The development system of claim 9 wherein said guidemeans guides a part of said excess developer and a part of saidadditional toner directly to said sump.
 11. The structure as recited inclaim 1 wherein said rotatable member comprises a roller and a permanentmagnet.